Conversion of a thermal energy into an electric energy by utilizing a Seebeck effect of a material is referred to as thermoelectric conversion and a device realizing the thermoelectric conversion is a thermoelectric conversion element. The material used for the thermoelectric conversion element is referred to as a thermoelectric conversion material and there is an index for evaluating the efficiency of thermoelectric conversion: Z=S2σ/κ, in which S is a Seebeck coefficient, σ is an electric conductivity, and κ is a thermal conductivity.
Thermoelectric conversion materials known so far include the followings.
(1) Semiconductor compounds such as Bi—Te, Si—Ge, and Zn—Sb, and compounds having a Skutterudite structure.
(2) Oxides typically represented by NaCoO2.
(3) Compounds having a half-Heusler structure such as ZrNiSn.
The Seebeck effect occurring in the materials described above is a phenomenon that electric charges move by a temperature gradient to generate current or voltage. On the other hand, patent document 1 discloses a Seebeck effect that occurs when a temperature gradient exerts on a spin to generate a current. When a thermal gradient is applied to a general ferromagnetic material such as NiFe, up-spin and down-spin in NiFe form currents in the directions opposite to each other relative to the direction of the temperature gradient. Then, when a material film such as Pt having a large spin-orbit interaction is attached to one of ends in the direction of the temperature gradient of the ferroelectric material, voltage (current) is generated in a direction perpendicular to the temperature gradient in Pt. This is referred to as a spin Seebeck effect.